Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
. .
This invention relates to an improved air knife such
as is used, for example, in coating a traveling paper web. It
is very important that the gap between the lips defining the air
knife orifice be accurately maintained at a uniform distance across
the entire width of the orifice. Since the gap is normally quite
narrow (i.e. about 0.030 inch), such factors as small deflections
of the lips, layers of built-up coating from the coating operation
and material removed from the lips when cleaning them, can cause
relatively great changes in the orifice gap. This is detrimental
to the function of the air knife which is to direct a steady,
uniform jet of air against a freshly coated web to evenly meter and
smooth the coating on the web across its entire width.
A problem typical of prior air knives is that they were
con~tructed with adjustable screws extending within the body member
between their lips. This necessitated the air to flow around the
adjusting screws before leaving the slotted orifice. Such an
arrangement is shown in U. S. Patent 2,139,628. The adjustment
screws cau8ed some interruption or turbulence in the stream of air
leaving the orifice across the air knife width.
Another problem ancillary to the prior design, which in
e8sence i9 still being used, relates to the manner in which the
gap between lips is adjusted to remain constant in the cross
machine direction. Over a period of time, coating builds up on
the lips and is removed by scraping. This produces slight defor-
mities on the surfaces of the lip tips which is compensated for
by tightening the adjustment screws extending between the lips.
Eventually, the lips become warped from the constant forces
exerted by the adjustment screws. In addition, after repeated
adjustments, the threaded contact between the screws and their
mounting in the lips becomes loose which makes it more difficult
than ever to maintain the lip gap within predetermined limits.
At the final stages of such looseness in the threaded mountings,
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the lips will move rapidly enough to chatter at which time all
semblance of accurate control of the lip gap vanishes.
When the lips of such prior design air knives had been
worn by several scrappings and deformed by continued tightening
of the adjustment screws on the top lip, they had to be disregard-
ed becuase they could not be refinished and still maintain the
orifice gap within the desired dimensions across the width of the
air knife. This is both costly and time consuming since the lips,
then as now, are made of stainless steel and must be accurately
machined and finished.
Still another problem with such prior air knife designs
relates to the fact that the top lip had to be slotted in order
to permit both lateral and pivotal adjustment to adjust the gap
relative to the stationary lower lip. Even though washers were
positioned over the slots, some air would inevitably leak pass
to mix with the coating material and cause misting.
SUMMARY OF THE INVENTION
This air knife has at least one lip which i8 adjustably
mounted to slide on the air knife body and be positioned by a
plurality of cam plugs. The lower lip is also designed to be
slidably extended, such as by screws extending through slots in
the lip, but is not necessarily equipped with cam plugs. Each of
the cam plugs operates in the same manner. The cam plugs are
aligned along the length of the air knife body which, in operation,
extends the width of the coater. The lip is positionable by the
cams without requiring any screws or other mounting members to
extend between the lips within the air knife body and thereby
interfere with the flow of air from the slotted orifice. In -
addition, the movable lip is not pivoted so it is not deformed by
the force of any adjustment screws.
Since each relatively small section across the width of
the movable lip is accurately positionable by the cams, it can be
cleaned, scraped or refinished many times while maintaining the
gap spacing within desired dimensional limits across the width
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of the air knife. In addition, the lip can be designed with a
wear resistant tip that would require less adjustment and re-
finishing over a period of time.
If desired, both lips can be made adjustable by cam
plugs. This will increase the initial cost, but will also greatly
increase the life and adjustability of the lips.
No slots extend through the walls of the air knife,
thereby precluding the possibility of misting.
Adjustment is strictly by lateral movement of the lip
(either top or bottom lip) relative to the body member, so no
bending of the lip is required. Further, the cam positioned lip
is secured to the body member by screws which are not associated
with the cam plugs so there i8 less opportunity for the threaded
connections to become loosened when the lip position is adjusted.
Accordingly it is an object of this invention to provide
an air knife having at least one cam adjustable lip.
Another object of the invention is to provide an air
knifé having an adjustable lip, but which requires no lip adjusting
or mounting structure which interferes with the passage of air out
of the slotted orifice.
Another object is to provide an air knife having an
adjustable lip which can be cleaned, scrapped and adjusted many
more times, compared to prior air knife lips, before it needs to
be replaced.
An advantage of this invention is the uniformity in
the stream of air emitted from the slotted orifice.
Other objects, features and advantages of the invention
will become apparent to those skilled in the art when the figures
are observed in conjunction with the description of the preferred
embodiment-
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross section side elevational view of a
prior art air knife showing the pivotable top lip with the mount-
ing and adjustment screws extending through the body between the
lips .
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Figure 2 is a plan view of the air knife of this
invention showing the cam plugs and screws securing the lip onto
the body.
Figure 3 is a cross section side elevational view of
the air knife through section "A"-"A" in figure 2.
Figure 3A i8 a cross section side elevational view
similar to figure 3, but showing both top and bottom lips being
locatable by cam plugs.
Figure 4 is an elevational view of a cam plug.
Figure 5 is a top view of the cam plug shown on figure
4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
. . _ . .
The prior art air knife as shown in figure 1, serves
to clearly illustrate the distinctions and advantages of this ~
invention. In the prior style of air knife 10, the top lip 12 ~ -
i8 initially notched at 14 so that the force applied on it by
the nuts 16 on adjusting screws 18 pivot and bend it at a known
location 14 when adjusting the gap 22 as it extends across the
width of the air knife. The term "width" as used here refers to
the long, axial dimension of the air knife which extends parallel
to the tip edge 21 of its lip 12. Since the air knife extends
transversely across the traveling web as it is being coated, the
"width" of the air knife extends across the width of the traveling
web.
Air emitting from orifice gap 22 must pass over the
adjusting screws 18 which are spaced at about 4 inch centers
along the width of the air knife. This interrupts the continuity
of the air stream which means the smoothing and metering action
of the air against the freshly coated web may not be as uniform
as desired.
Paper coating material contains abrasives such as
titanium dioxide and clay. In a paper making machine with an on-
machine coater, sheet breaks cften cause the sheet (which might be
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paper board) to wad up or lash out in whip-like action. This
causes the paper to strike the lip tip 20 with considerable force
which can cause nicks and distortions in the lip tip and edge 21.
In addition, the lip tip 20 gradually becomes incrusted with coating
material over a period of time. About once a month, therefore, it
needs to be removed for cleaning and refinishing.
As the lip tip is worn away in the refinishing process
to make it straight and smooth, the notch 14 is moved further
down towards the tip. Subsequent adjustments of nuts 16 on screws
18 therefore tend to bend the top lip in a position more in the
middle of the lip which tends to accentuate distortion at the top
lip tip 20.
This dual bending and lateral movement of the top lip
is necessary to correct for distortions in the lower, stationary
lip also. There are slots in the top lip 12 which allow the
refinished lip to be relocated down further toward the orifice
gap 22. When the notch 14 shifts downwardly as the lip is perio-
dically refinished, the slots are more difficult to cover with
curved washer 24 and the escaping air mixes with the coating
material in the immsdiate vicinity to cause misting. This misting
impairs the quality of the coated paper it contacts.
As shown in figures 2 and 3, the air knife of this
invention utilizes a plurality of cam p~ugs 26 which are positioned
between the top lip 28 and the body member 29. Edge 21 is posi-
tioned adjacent rotating roll 6. The cam plug 26 is more clearly
shown in Figures 4 and 5. A cylindrical pilot hub 30 extends
beneath a cylindrical flange 32. A cap 34 having many sides ex-
tends above the flange 32 on the opposite side from the pilot hub
to enable a wrench to be applied to turn the cam plug. Cap 34
is concentric with flange 32, but hub 30 is offset so that rota-
tion about its axis of rotation 31 causes the cylindrical cam
surface 36 on the peripheral edge of flange 32 to define a path
which reciprocates as a cam plug is turned.
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Referring again to figures 2 and 3, cam plug 26 is
rotatably mounted in the air knife body member 29. Top lip 28
has a surface 40 which is adapted to slide over a corresponding
surface 41 on body member 29. A cylindrical recessed opening
46 i8 formed in the underside of the top lip. This opening does
not extend through the top lip, but stops short to form an in-
wardly extending rim 44 which prevents the cam plug from coming
out when the top lip is positioned over the body member 29. Cap
34 extends through rim 44 above the top lip surface. Cylindrical `
opening 46 is of a diameter slightly larger than the longest
radial distance of cam surface 36 from the axis of rotation 31 of
cam plug 26 (figure 5) so that the cam plug can be rotated in a
complete circle within opening 46 if desired. This configuration
also permits the top lip to be moved forwards toward the orifice
gap 22 without moving it sideways.
The ends of the air knife are plates 48, 49 which are
held in place by toggle arms ~hown generally at 50, 51. These
end plates and toggle arms as well as the means for supplying air
to the air knife form no part of the invention and will not be
discussed further in detail.
Alternating with the cam plugs along the width of the
air knife body are a plurality of screws 54, each of which passes
through a corresponding slot 52 in the top lip 28. Slots 52
extend toward and away from orifice gap 22 to permit the top lip
to 81ide toward gap 22 via surfaces 40, 41 when its tip 20 has
been shortened during cleaning and refinishing. A washer 56 is
positioned over each slot 52. Since the slots 52 are located
over that portion of the body member extending immediately beneath,
and the tapped holes for screws 54 do not extend through body
member 29, no air escapes past slots 52 to cause misting.
A bottom lip 58 cooperates with top lip 28 to form the
orifice gap 22 which extends the width of the air knife. Bottom
lip 58 is shown with screws 54 mounting it to the air knife body
through slots 52 in the same manner as the screws 54 secure the top
lip. Figure 3A shows both top and bottom lips 28, 58 positionable
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by cam plugs and secured by screws in identical manner. This
orifice gap is commonly set at about 0.030 0.045 inch, but may
vary depending on the conditions of operation.
When the gap 22 needs adjustment, screws 54 are loosened.
A wrench is then applied to cap 34 to turn a cam plug 26. The cam
surface 36 bears against the inner cylindrical pressure surface
47 of opening 46 to ~rge the top lip 28 to slide toward the
orifice gap 22. A feeler gage is used to determine the proper
gap at each point along the width. This procedure is started at
the middle of the air knife and proceeds outwardly with cam plugs
in both directions.
This gap adjustment procedure is delicate, but greatly
facilitated by the cam plugs which operate to smoothly change
the gap spacing and accurately locate the tip edge 21 at each
position across the air knife width. If only one lip is cam
positioned, it might be characterized as being accurately
adjustable while the other lip would then be comparatively
characterized as being coarsely adjustable.
The gap spacing is influenced by other factors besides
wear. The beam deflection across the width of the air knife
causes some differences in the gap spacing at different locations
along the span. Thus, independent of wear, the cam plugs can
easily compensate for slight local differences in the gap spacing
caused by deflection. As each cam plug adjusts the gap in its
vicinity to the desired setting, the adjacent screws are initially
lightly tightened to secure the top lip in place until uniform
gap established over entire width is then securely tightened.
The gap can thus be adjusted many times to compensate
for much wear since the top lip merely slides along the surface
41 of the body member and is not required to pivot or be bent by
adjustment screws. The lower lip 58 need only be extended by
loosening screws 54, if it is not equipped with cam plugs. Fine
adjustment of the orifice gap spacing can then be done by the cam
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plugs on the top lip. If both lips are cam positioned to locate
their lip tip edges (Figure 3A), the gap adjustment procedure is
the same for each lip.
The amount of material that can be removed from the
lip tip is only limited from a practical standpoint by the
distance the lip can be moved forward by the cam action of the -
cam plugs. It is possible that the lip tip can be made of a .
hard, wear resistant material, such as a ceramic, which would
eliminate refinishing operations and merely require replacement
of lip if damaged.
